Methods of this kind are used in motor vehicles for voice-supported duplex telephony or for supporting voice input-controlled electronic or electrical components. The fundamental difficulty that arises is that, depending on the particular operating state, there is background noise in the motor vehicle. This masks the voice commands. Intercom and two-way intercom systems in motor vehicles are mainly advantageously used in large vehicles, minibusses and the like. However, they can also be used in normal passenger cars. When using voice-controlled input units for electrical components in motor vehicles, it is still very important for the background noise to be suppressed or for the voice command to be filtered out.
Thus, a voice-recognition device for a motor vehicle is described in European Patent Application No. 0 078 014, where the status of engine operation and/or motor vehicle movement is signaled or fed in, via sensors, to the amplifier system of the voice-recognition device. Based on this, a noise-level control is then used to attempt to filter out the voice command from the background noise.
A filtering operation is described in PCT International Published Patent Application No. WO 97/34290, where periodic interfering noise signals are filtered out by determining their periods and by using a generator to interfere with them, so that the voice signal remains.
In German Published Patent Application No. 197 05 471, it is described to support a voice recognition with the aid of transversal filtering.
In German Published Patent Application No. 41 06 405, a method is described for subtracting noise from the voice signal, a multiplicity of microphones being used. A duplex telephony device having a plurality of microphones is discussed in German Published Patent Application No. 199 58 836.
In German Published Patent Application No. 39 25 589, it is described to use a multiple microphone system, where, in motor vehicle applications, one of the microphones is placed in the engine compartment and one other microphone in the passenger compartment. A subtraction of both signals then follows. The disadvantage in this context is that only the engine noise or the actual running noise of the vehicle itself is subtracted from the total signal in the passenger compartment. Specific secondary noises are disregarded in this case. Also lacking is a feedback suppression. Everywhere that microphones and loudspeakers are placed in an acoustically coupleable vicinity, the acoustic signal that is extracted, coupled out or decoupled at the loudspeaker is fed back into the microphone. The result is a so-called feedback, and a subsequent overmodulation. Methods for avoiding such an overmodulation are described in European Published Patent Application No. 1 077 013, PCT International Published Patent Application No. WO 02/069487, and PCT International Published Patent Application No. WO 02/21817.
It is an object of the present invention to provide a method and a device that may improve the verbal communication among the occupants of a vehicle.